Jaw advancing mechanism



Filed Dec. 2, 1957 INVENTORS. ARNOLD SCHINDEL HENRY 'TROEGER .ATTORNEY i JAW ADVANCING MECHANISM Arnold.Schindel, Fairlawn, N.J and Henry Troeger,

Cooperstown, N.Y., assignors to Bendix Aviation Corporation, Utica, N.Y., a corporation of Delaware 'Ihisinvention relates to high speed starters and more United States ,l atent particularly concerns such starters which have" starter jaw advancement.

Inatypical starter having starter jaw advancement,

an annular spline nut having an. internal helical thread is the end member of the starter power train which is axially-fixed. An annular starter jawhas an external helical thread which is mated into the spline nut. Rotation of the spline nut causes the starter jaw to advance into engagement with the engine jaw provided there is a frictional drag on. the starter jaw so that the starter jaw will axially-advance through the helical connection. Such a'jaw advancing arrangement is disclosed in the pending Troeger US. patent application 'S.N. 542,147 (filed Octo ber 24, 1955, and assigned to the same assignee as the present application); This arrangement has a pivoted arcuate fly-weight which is spring-biased to apply frictional drag to the starter jaw for advancement The frictional drag is removed after the associated jet engine is started due to increasing centrifugal action on the fly weight. Since the fly weight is simply a pivoted arcuate member, the friction applied varies as the speed.

object of thepresent invention is to provide an improved starter jaw advancing mechanism in a high speed starter which applies aconstant friction until a predeter- .mined speed is reached whereby the reliability of engagement is improved. l A further object is to provide an improved centrifugall y operated friction mechanism withina helicallyadvanced starter jaw which applies a constant friction to the starter jaw until starting speed is reached when centrifugal' means will remove the friction;

v Realization of the above objects and the advantages and features of this invention will be apparent from the following description and the accompanying drawing in which: 7

Fig. l is a longitudinal cross-sectional view of apart ofcombustionturbine starter embodying the invention and shows the starter jaw out of engagement with the engine jaw and shows internal details of the friction mechanism on the line A--A of Fig. 2 and Fig. 2 is an enlarged transverse crosssection along the line B-B of Fig. 1 and shows the details of the centrifu- 'gally-operated friction mechanism which includes a short pivoted friction member spring-biased into contact with the starter jaw and a longer pivoted element which is arranged to move the friction member out. of contact at starter cut-0E speed. 9 I

In Fig. l, the parts of an aircraft jet engine arid of the starter which are adjacent the engine jaw and the starter jaware shown. The engine housing has a mounting flange'l l which abutsan engine drive pad 12 and is suitably connected thereto by bolts or other fastening helical connection.

'(not shown) rotates starter barrel member 17 at the exterior of the starter section by means of a reduction gear train (not shown). The barrel member 17 in the disclosed embodiment is the output rotating cage of a twostage planetary gear system. .Rotation of barrel 17 causes "rotation of screw nut 18 which is interior of the barrel 17 since these two members are connected by clutch 19. Clutch 19' is conventional and is comprised of a multiplicity of discs which are interleaved and are urged together by Belleville springs 20. Clutch 19 provides for slippage under rapid acceleration conditions at the start of the cranking cycle.

The annular screw nut 18 is supported at its right end by hearing 22 which, in turn, is carried by a stationary axial shaft member 23 of the starter. Member 23 in the disclosed embodiment is the support for the first stage planetary gearing. Bearing 22 is locked in a position by clamping nut 24 which is threaded over the outer or left end of support 23. Thein'ner end of clamping nut '24 bears against a spacer ring 25 which, in turn, abuts the inner race of the bearing 22. Screw nut 18 has internal helical threads or splines 26 which engage with corresponding splines 27 on the external surface of the annular starter jaw member 31. Jaw member 31 has an axiallyextending ring of jaw teeth 32 at its left end. Upon counterclockwise rotation (as seen from the right) and advancement of starter jaw 31 over the helical connection, starter jaw teeth 32 engage corresponding jaw teeth on the right face of the transverse flange of the engine jaw 15. With such jaw engagement, cranking of the engine shaft 16 from the starter power source is provided. 1

For jaw advancement, friction is applied by a plurality of friction mechanisms to the inside surface of the annular starter jaw 31 so that jaw 31 will advance over the A normal pressure at the mating helical splines 26, 27 results so that starter jaw 31 ad'- vances to the left rather than rotates with the screw nut in the position shown on the drawing. Thus, the frictional resistance causes the starter jaw to advance to the left and to engage the engine jaw 15. The friction mechanisms are housed within a'cup-like yoke 33 which extends inwardly. from the transverse inner wall or flange of the engine jaw 15 to between starter jaw 31 and nut 24 or shaft 23. The yoke 33 is threaded into the inner part of the engine jaw 15 and is also connected thereto by several pins 30. The friction mechanisms will now be described with reference to Figs. 1 and 2.

The cup-like yoke 33 has three radial slots, each housing an identical friction mechanism which is supported by pins extending axially between the transverse sidewalls of the radial slots in yoke 33. A first fixed pin 34 is stationary within each radial slot since it is supported at its ends the sidewalls thereof. End pin 34 provides support for one end of leaf springs 35 which arepositioned on both sides of a short arcuate friction shoe 36. Shoe 36 is pivoted at one end on pin 34 and its other end is forked or formed with two arms and a radial groove. The reaction point for the other ends of the springs 35 is a. stationary pin 37 which is also fixed in yoke 33. The springs 35 have their ends bent partially around pins 34 and 37 and are arranged to bias the free forked end of friction shoe 36 outwardly beyond the periphery of'yoke 33'into contact with starter jaw 31. Center pin 37 also serves as a pivot point for an arcuate fly weight or centrifugal arm 38. Arm 38 has a long heavy end to the right of pin 37 and short light end to the left of pin 37 as seen in the upper left part of the Fig. 2.

The centers of springs 35 react against projecting ends of floating. pin 39. Pin 39 is fixed in the forked end of friction shoe 36. Thus,; the springs cause the forked end of friction shoe 36 to be urged into contact with the innormal force and creates friction between starter jaw 31 and the friction shoe 36 when starter jaw 31 attempts to rotate relative to the yoke 33.

of spring 42. Spring'42 is attached 'to"the walls between the radial slots in the yoke 33 bymea'ns of screw 43.

The reaction load of spring42'is taken by the long end of the centrifugal arm 36 bearing against an end pin 45 which is fixed in yoke 33. An enlarged hole 46 in arm 36 is mated with pin 45. The short endof the centrifugal arm '38 projects into the radial groove in shoe 3 6 and has pin 39 extending therethrough. Pin 39' is received in an enlarged hole 48 in the short end of the centrif ugal arm-'38. The short end or tongue 'of the centrifugal arm 36 is thuspartially housed in the forkedpart of the friction shoe v36. The long end of arm 38 is sufficiently wide and long (or otherwise Weighted) so that it will move outwardly at starter cut-off speed against opposing forces. It is to be no'ted that in normal positioning for jaw advancement, as shown in :Figs. 1 and 2, the pin 39 is uniformly spaced from the edge of the opening 48 in the centrifugal arm '38 and that the pin 45 bears against the outer edge of the hole 46 in centrifugal arm 38. It is apparent that centrifugal arm 38 has an inwardly-tensioned end adjacent spring 42 which is adapted to move outwardly under centrifugal action.

This end is appreciably longer and heavier than the other shorter and narrower end ofarm 38 which will be pivoted radially inward. The friction shoe 36 is made of a light material, such as aluminum, so that the centrifugal forces which it generates will be small when compared to the heavier end of steel arm 38. The pin 45 also serves as a stop and limits the outward travel of centrifugal arm 38 when the inner side of enlargedhole 46 bears against this pin 45 so that arm 38 will not project'beyond the yoke 33.

Referring to Fig. 1 it can be seen that the yoke 33 supported at the inner end by a carbon bushing 51wh'ich is contained at the inner end of the yoke 33by a washer 52 and a spinning 53 of the right end of yoke 33. 'This bearingrides on locking nut 24 which is threaded on the starter axial shaft 23 and is locked thereon by 'a locking ring. Spring 61 is contained against the helical spline connection by lock ring 62. Spring 61 reacts on the helical spline of the starter jaw 31 causing it to be fully retracted and to remain outof engagement with the engine jaw 15 when the starter is inoperative or when the engine is overrunning the starter. Bearing 64 within the tubular shaft part of the engine jaw 15 is mounted on axial shaft 65 which, in turn, is contained in the interior of the stationary starter shaft 23 by heavy spring 66 hearing against a flange'on shaft 65. Spring 66 provides for some axial play of the engine jaw. in respect to the advancing starter jaw; Q

Inoperation, the barrel member 17 is' rotated and through clutch 1? causes rotation of screw nut 18-. Screw nut 18 .tends to rotate starter jaw 31 along with it in the position shown in the drawing due to the helical spline connection. The friction mechanisms are arranged to provide a retarding friction on the starter jaw 31 so that it advances for engagement with the teeth of the engine jaw 15. The spring-biased arcuate friction shoes 36 exert a normal pressure on the inside surface of starter jaw'31. The axial component of this normal force causes starter jaw 31 to advance. Upon initial contactofthe jaw teeth, the inertia load creates a high normal pressure at the helical splines 26, '27 which results in complete engagement of the jawteeth of the engineijaw. 15 and starter jaw 31. Since the engine is then driven byjthe starter, the engine is caused to accelerate. Ata predetermined speed approaching cut-offspeed, each of the arcuate actuator arms38 pivots about pin 37 so that the side surface of starter jaw'3-1. This loading creates a V jaw 31.

end adjacent friction shoe 36 moves inwardly. The other 36. After the outer wall of-the-enlargedhole 48 in arm v 38 contacts the pin 39, the frictionshoe 36 moved out of contact with the inner'surface of the start er jaw 31. The long end of arm 38 under centrifugal actionovercomes the spring forces and affects other centrifugal effects. Upon further increase in speed, the centrifugal arm 38 pivots outwardly further against spring 42 and further clears friction shoe 36 from possible contact with starter jaw 31. This action is limited by the long end of arm 38 having the inner wall of its enlarged limit hole 46 contacting stop pin 45. Thus, in'overrunning condition a t'high speeds, the fly weight 38 remains constrained from further pivoting by the positioning actionof I pin 45 and no friction force is applied during the period fly weight 38 is displaced while the engine is rotating'yoke 33. Before centrifugalarm' 38 is actuated, it is to be noted that springs 35 bearing upon pin 39 which is integral with friction shoe 36 causes shoe 36 to be biased against the inside of the helically-splined starter jaw 31. shoe provides a high friction surface where in contact with the starter jaw. After reaching starter cut-off speed, the starter is deactivated by conventional controls which are arranged to interrupt the energizing force to the starter turbine' at a predetermined speedthereof. This speed is normally such that the associated engine is operating under its own power. At this stage, the engine jaw 15 overmns the starter jaw 31 and by axial forces at the jaws, causes the starter jaw to be displaced out of engagement as is conventional. This action is helped by spring 61 which exerts a force against the left or outer end of the starter The return spring 61 furtherfunctions to prevent ratcheting of "the starter jaw 31 due ,to vibratory effects tending to move this jaw into engagement after the starter has been deactivated. In overrunning and since the jaw advancement friction has been removed, theonly constraint on the engine jaw 15 and yoke 33 is fromb'ear: ing 51 and bearing 64. A

'Upon deceleration of the engine jawand yoke construction to approximately cut-off speed, the centrifugal action onthe centrifugal arms 38 will decrease so that the long ends thereof moveradially inward. This radial movement is such that, below cut-off speed, friction shoes 36 again come into contact with the inner surface'of the starterjaw 31. However, since the-starter jaw 31 is not turning at this point, the friction created causes the starter jaw, if not so positioned by spring 61, to bedisplaced completely to the right and kept out ofengagement withthe engine jaw 15. At such time, should the starter be re-energized, frictional force will be available to cause re-advancement and re-engagement.

From the foregoing, it is apparent that the rotating starter jaw 31 is axially advanced into engagement by means of the arcuate friction shoes 36 which contact the inner surface of the starter jaw and are carried in radial slots in the cylindrical wall of the cup member 33;. .At starter cut-01f speed, the centrifugal arm 38 is pivoted mentof its short linked end, causes friction shoe 36 to be urged out of contact with the starter jaw 31. An important advantage of the present invention is that'the centrifugal force for the removal of the frictional force does not become operative until close to the starter cu-t-ofl speed. 7

Thus, the initial friction force is' not decreased untilthe starter is near cut-off speed when the centrifugal arm contacts floating pin 39. This arrangement gives improved operation over an element which combines the friction surface and the centrifugal weight in a single part since It is also to be noted that the light-weight friction a higher normal force with associated retarding tangential friction is available at speeds which are close to cutoff speed. This results in improved reliability of jaw engagement.

It is to be understood that persons skilled in the art can make changes in the disclosed embodiment of the invention without departing from the invention as set forth in the appended claims.

What is claimed is:

I. A high speed starter comprised'of a driving member helically splined to astarter jaw, friction means contacting said starter jaw arranged to cause said starter jaw to advance relative to said driving member when rotating, said friction means including friction shoe contacting said starter jaw and a centrifugally-actuated device connected to said friction shoe, said centrifugally-actuated device being restrained by a spring and being so constructed and arranged that it pivots outwardly a limited distance without moving said friction shoe and then further pivots outwardly at a predetermined speed to move said friction shoe out of contact with said starter jaw.

2. A high speed starter having a starter jaw helicallysplined to a screw nut in combination with the advancing mechanism comprised of a light-weight frictional member for engaging the interior of said jaw, a centrifugal ele-.

ment for displacing said frictional member, said frictional member being pivoted at one end to a stationary first pin and carrying a second pin at the other end, one end of said centrifugal element being loosely connected by said second pin, said centrifugal element being pivoted adjacent said one end, the other end of said centrifugal element being loosely connected to a stationary third pin and normally-urged inwardly by a spring into contact with said third pin, said spring providing a limited resistance to centrifugal movement of said other end of said element, said frictional member being spring-tensioned into frictional contact with said starter jaw, said centrifugal element being so arranged and connected that said other end thereof moves outwardly under centrifugal forces a limited distance before it begins moving said frictional member out of contact with said jaw.

3. In engine starter mechanism of the character described, including a rotatable nut member, a starter jaw helically splined in the nut member for rotation therewith, an engine jaw disposed in axial spaced relation to the starter jaw, a member carried by the engine jaw and projecting axially into the interior of the starter jaw, means contained in the member normally exerting a friction force upon the interior wall of thestarter jaw and effective to cause the latter to advance axially out of the nut into engagement with the engine jaw upon rotation of the nut member, the friction exerting means having a plurality of light-weight arms pivoted at one end in slots in the wall of the member and tensioned by springs into frictional engagement with the interior wall of the starter jaw member, actuator means on said member responsive to centrifugal force arranged to pivot said friction-exerting arms inwardly out of said engagement against said springs, said actuator means being loosely connected to said arms and further arranged so that it begins to pivot said arm after it has been moved a limited extent by centrifugal force.

4. In engine starter mechanism of the character described, including a rotatable screw nut member, a starter jaw helically splined in the nut member for rotation therewith, an engine jaw disposed in axial spaced relation to the starter jaw, a member carried by the engine jaw and projecting axially into the interior of the starter jaw, friction means contained in the member normally exerting a friction force upon the interior wall of the starter jaw and eifective to cause the latter to advance axially out of the nut member, the friction exerting means including a plurality of light weight arcuate friction shoes, each rotatable at one end on a first pin in a radial slot in the Walls of the member, centrifugal arms pivoted for out- Ward movement on a second pin fixed at its ends'in opposed walls of each of the slots, means to limit the extent of such pivoting by said arms, the free end of each friction shoe, carrying a. third pin loosely-connected to one end of each of said arms, spring means mounted onsaid' first and second pins and tensioned against said third .pin, and tensioning the shoes in an angular direction .so that the free, end of the shoe frictionally engages the rotated by the starter jaw subsequent to engagement so that the frictional force of the arcuate shoes is released from the member when each of said arms contacts said third pin.

5. A starter for a turbine engine comprised of an engine jaw having splines adapted for connection to the shaft of a turbine engine, said engine jaw having aring of axially-extending engine jaw teeth, a starter jaw member of annular shape havinga ring of axially-extending starter jaw teeth constructed to engage said engine jaw teeth, a rotatable annular cage connected interiorly to an annular screw nut, said nut being connected by a helical spline connection to said annular starter jaw, a cup-like yoke connected to said engine jaw and extending between said starter jaw member and the outer part of said starter shaft, the cylindrical wall of said yoke having radial slots, a friction mechanism in each of said slots for frictionally contacting the interior surface of said annular starter jaw to cause axial advancement thereof,

said friction mechanism including a short arcuate fric-.

tion shoe and an arcuate centrifugal arm, one end of said shoe being pivotally-mounted on a first pivot pin which extends between the side walls of said slots, said centrifugal arm having one end loosely connected to the other end of said shoe and being pivotally mounted on a second pivot pin fastened to said side walls, spring means urging the other end of said arm radially inwardly, tensioning means urging said friction shoe radially outward so that said shoe normally contacts the inner surface of said starter jaw, said centrifugal arm having its spring-tensioned end heavier than its loosely connected end whereby, when its spring-tensioned end moves outwardly by centrifugal action above a predetermined speed, the loosely-connected end will be urged inwardly, and the parts of said friction mechanism being so arranged and proportioned that said shoe will be moved out of contact with said starter jaw by said centrifugal arm at a predetermined speed and after a limited pivoting of said centrifugal arm.

6. A starter for a turbine engine comprised of an engine jaw having splines adapted for connection to the shaft of a turbine engine, said engine jaw having a ring of axially-extending engine jaw teeth, a starter jaw member of annular shape having a ring of axially-extending starter jaw teeth constructed to engage said engine jaw teeth, a rotatable annular cage connected interiorly by a spring-biased clutch pack to an annular screw nut, said nut being connected by a helical spline connection to said annular starter jaw, said screw nut being rotatably mounted on the inner part of a stationary axial starter shaft member, a cup-like yoke connected to said engine jaw and extending between said starter jaw member and the outer part of said starter shaft, the cylindrical wall of said yoke having radial slots, a bearing between the inner end of the cylindrical wall of said yoke and said stationary starter shaft member, a friction mechanism in each of said slots for frictionally contacting the interior surface of said annular starter jaw to cause axial advancement thereof, said friction mechanism including a short arcuate friction shoe and an arcuate centrifugal arm, one end of said shoe being pivotally-mounted on a first pivot pin which extends between the side walls of said slots, the other end of said shoe being forked and having pin axially-extending between the arms of said tforked other end of said shoe, said centrifugal arm having a tongue end loosely connected by an enlarged ho le to the pin in said forked end of said shoe and being pivotally mounted on a second pivot pin fastened to said side walls, the other end of said arm having an enlarged opening through which a fixed stop pin projects, spring means urging said other end of said arm radially inwardly so that the outer edge of said enlarged opening abuts said stop pin, tensioning means urging said friction shoe radially outward so that said shoe contacts the inner surface of said starter jaw below a predetermined speed, said friction shoe being made of a light weight metal, the spring-tensioned end of said arm being constructed heavier than its tongue end whereby, when the springtensionedend moves outwardly, byl centrifugal faction above a predetermined rspeedgth tongue end will be, urged inwardly, and the partsrof said friction mechanism ,beingvso arranged and proportioned that said shoe will be movedoutof contact with said startertjawby said centrifugal arm at a predetermined speed "and after a limited pivoting of said centrifugal arm. 7

2,398,087 Dodge Apr. 9} 1946 Gordon July 3, 1951 

